8.10 Internal Database

The predicates described in this section were introduced in early implementations of Prolog to provide efficient means of performing operations on large quantities of data. The introduction of indexed dynamic predicates have rendered these predicates obsolete, and the sole purpose of providing them is to support existing code. There is no reason whatsoever to use them in new code.

These predicates store arbitrary terms in the database without interfering with the clauses that make up the program. The terms that are stored in this way can subsequently be retrieved via the key on which they were stored. Many terms may be stored on the same key, and they can be individually accessed by pattern matching. Alternatively, access can be achieved via a special identifier, which uniquely identifies each recorded term and which is returned when the term is stored.

recorded(?Key,?Term,?Ref) obsolescent

The database is searched for terms recorded under the key Key. These terms are successively unified with Term in the order they occur in the database. At the same time, Ref is unified with the database reference to the recorded item. If the key is instantiated to a compound term, only its principal functor is significant. If the key is uninstantiated, all terms in the database are successively unified with Term in the order they occur.

recorda(+Key,?Term,-Ref) obsolescent

The term Term is recorded in the database as the first item for the key Key, where Ref is its database reference. The key must be given, and only its principal functor is significant. Any uninstantiated variables in the Term will be replaced by new private variables, along with copies of any subgoals blocked on these variables (see Procedural).

recordz(+Key,?Term,-Ref) obsolescent

Like recorda/3, except that the new term becomes the last item for the key Key.

current_key(?KeyName,?KeyTerm) obsolescent

KeyTerm is the most general form of the key for a currently recorded term, and KeyName is the name of that key. This predicate can be used to enumerate in undefined order all keys for currently recorded terms through backtracking.